KINETIC, DYNAMIC, AND PATHWAY STUDIES OF GLYCEROL METABOLISM BY KLEBSIELLA-PNEUMONIAE IN ANAEROBIC CONTINUOUS-CULTURE .1. THE PHENOMENA ANDCHARACTERIZATION OF OSCILLATION AND HYSTERESIS

Oscillation and hysteresis phenomena are observed in the anaerobic con tinuous fermentation of glycerol by Klebsiella pneumoniae in long-term cultivations under a variety of conditions. In this work, the conditi ons for the occurrence of these phenomena are reported and the pattern s of cell growth and metabolism under oscillation are characterized. D uring an oscillation period, the formation rates of CO2, H-2, and form ate and the consumption rate of alkali periodically pass values of max ima and minima, the latter being close to zero. The formation of bioma ss and fermentation products such as 1,3-propanediol, acetate, and eth anol also undergo periodic changes which shift maxima and minima. Sust ained oscillation occurs only under conditions of substrate excess wit hin a distinct regime. At pH 7.0, it is only found at dilution rates a bove 0.15 h(-1) under the experimental conditions. At lower pH values, oscillations are more likely to happen, even at a relatively low dilu tion rate and low substrate excess. Whereas the amplitude of oscillati ons at pH 7.0 depends on both the dilution rate and the residual glyce rol concentration (C-Glyc) the interval of oscillations appears to be only a function of C-Glyc. An increase of C-Glyc in culture damps the oscillation and leads to its disappearance at C-Glyc = 1100 to 1200 mm ol/L (pH 7.0). The operation mode was also found to be an important pa rameter in determining the stability and actual state of the culture, resulting in hysteresis under certain conditions, particularly at low pH values. Generally, a large perturbation of cultivation conditions t ends to cause oscillation and hysteresis. The results unambiguously de monstrate that the oscillation and hysteresis phenomena shown in this work are bound to genuine metabolic fluctuations of the microorganism. They reveal several differences and new features compared with those reported in the literature and cannot be readily explained by the mech anisms known so far. (C) 1996 John Wiley & Sons, Inc.